This invention relates to a method of fabricating a bottle-shaped container of saturated polyester and, more particularly, to a method of fabricating a bottle-shaped container which provides superior mechanical strength, very low degrees of age and high temperature deformation, and high dimensional stability.
A transparent thin-walled blow-molded container of biaxially oriented plastic is manufactured by heating a cylindrical piece or parison having a bottom made of saturated polyester such as polyethylene terephthalate to a temperature in the range between the glass transition point and the crystallization temperature of the parison, loading the heated piece into a fully automatic rotary multi-station type blow molding machine via a loading unit, and then laterally and longitudinally biaxially-orienting the piece in the blowing mold. Since the container of saturated polyester thus biaxially oriented has superior transparency, low water and gas per meabilities and is non-toxic, it has a wide range of applications for use as a container in the fields of liquid condiments, soft drinks, alcoholic drinks, etc.
While a container of biaxially oriented saturated polyester is arranged with molecular chains and is formed with microcrystals to improve the mechanical strength and gas permeability resistance, it simultaneously retains remarkable strain in the interior of the wall thereof. When the age strain is exposed to an environmental temperature at or above, for example, approx. 70.degree. C., the strain tends to be released, causing the container to shrink. Such shrinking takes place when the container is cooled upon removal of the molded container from the mold, thereby causing severe problems with the dimensional stability of the container.